1. Field of the Invention
The present invention relates to the preparation of homogeneous block copolyetheramides which are flexible at low temperatures, have high melting points and low glass transition temperatures, and the melt viscosities of which are such as to permit the facile shaping thereof, e.g., by injection molding.
2. Description of the Prior Art
In published French Application No. 83/10,939, assignee to the assignee hereof, novel homogeneous block copolyetheramides are described having, in particular, a high crystallinity as to provide high melting points and good thermo-mechanical resistance, a glass transition temperature which is as low as possible as to impart high flexibility and elasticity at temperatures as low as those equal to or below -20.degree. C., and a high melt viscosity compatible with the facile shaping thereof, e.g., in the fields of injection molding and extrusion.
The prior art noted in the aforesaid '939 French application includes U.S. Pat. No. 4,218,351, which describes thermosplastic elastomers consisting of copolyetheramides. The focus of this patent is a general class of copolyetheramides which are produced by direct reaction among three types of components, each having functional groups capable of taking part in a reaction for the formation of amide groups. The first component (i) is selected from among a short-chain dicarboxylic acid, a short-chain diamine, a short-chain lactam, a short-chain aminoacid and a mixture of two or more of these species with each other; the second component (ii) is a fatty acid dimer or an amino derivative of a fatty acid dimer; the third component (iii) is a polyoxyalkylenediamine or a polyoxyalkylenedicarboxylic acid. The components taking part in the reaction are selected such as to contribute substantially equal amounts of NH.sub.2 and COOH groups to the reaction medium. From the examples in said '351 patent, it will be noted that the copolyetheramides which are actually prepared are essentially produced by reaction (i) of a mixture of a short-chain diacid or a short-chain diamine or a mixture of a lactam and a short-chain diacid or a short-chain diamine with a reactant of type (ii) and a reactant of type (iii). The copolyetheramides prepared in this manner have interesting properties, especially low-temperature flexibility, which is responsible for the good resilience properties attributed thereto. However, their low melt viscosity, which is generally below 100 poises at 232.degree. C., does not permit them to be used as adhesives. Now, in the fields of plastics molding and extrusion there is a need for materials having a sufficiently high melt viscosity to enable same to be injection molded or extruded in a suitable manner. The prior art is conspicuously silent as regards means for the preparation, beginning with the reaction mixtures in accordance with the teaching of said '351 patent, of copolyetheramides having a sufficiently high melt viscosity as to be useful as technical plastics.
The French Application No. 83/10,939 features copolyetheramides for the purpose of providing polymers for molding and extrusion, having a high melt viscosity, and additionally having a high flexibility down to temperatures as low as those equal to or below -20.degree. C.
More specifically, said '939 French application features homogeneous block copolyetheramides having, in particular, a melting or softening point of at least 170.degree. C., a glass transition temperature measured at ZHE not exceeding -5.degree. C. and a melt viscosity of at least 500 poises, said copolyetheramides being prepared according to the following operating procedure, in which:
(a) a lactam containing from 4 to 12 carbon atoms is mixed with a solution of a salt of a fatty acid dimer and a polyoxyalkylenediamine in a solvent medium based on a mixture of water with an aliphatic alcohol containing fewer than 5 carbon atoms, a water/alcohol/lactam mixture (both the alcohol and the lactam employed being as above defined) and of the lactam itself in a molten state or, when the lactam is water-soluble, a water/lactam mixture;
(b) the stoichiometry of the said salt has been established beforehand by measuring the pH of the salt solution in a solvent mixture based on water and at least one compound selected from among an aliphatic alcohol, an aliphatic diol or a lactam (both the alcohol and the lactam employed also being as above defined, the aliphatic diol containing from 2 to 6 carbon atoms) and by adjusting the composition of the said salt such that the pH attains, within .+-.0.05 pH unit, the pH value at the equivalence point, the mixing of the salt solution with the lactam being capable of being omitted when the solution of salt in the solvent medium based on a water/alcohol/lactam mixture, a water/lactam mixture or the lactam itself in the molten state contains sufficient lactam to produce the copolyetheramide of the required composition;
(c) a catalyst consisting of an inorganic oxyacid or an organic oxyacid other than a carboxylic acid, at least one of the acid groups of which, when there are more than one, has an ionization constant pKa in water at 25.degree. C. equal to or below 4, is then added to the reaction mixture; and
(d) the entire reaction mass is then subjected to heating to cause the lactam to react with the salt.
Referring to melt viscosity, said '939 French application indicates that it is measured at 230.degree. C., under a shear gradient of 10 s.sup.-1 using a Davenport rheometer in the case of copolyetheramides produced from lactams containing 6 to 12 carbon atoms; in the case of copolyetheramides produced from lactams containing 4 to 5 carbon atoms, the melt viscosity is measured as indicated above, but at 260.degree. C.